Effect of Broccoli Residue and Wheat Straw Addition on Nitrous Oxide Emissions in Silt Loam Soil

Nitrous oxide (N2O) is one of the main greenhouse gases and its emissions from vegetable production systems have brought a sustainability challenge. The objective of this study was to evaluate the potential of reducing N2O emissions from silt loam soil by mixing nitrogen (N)-rich broccoli (Brassica oleracea var. italica) residue with wheat straw or water-washed wheat straw. An experiment was conducted in randomized complete block design with five treatments; unamended or control (BS), wheat straw (+S), broccoli residue (+CR), broccoli residue and wheat straw (+CR+S) and broccoli residue and washed wheat straw (+CR+Sw) and was replicated four times. The +CR and +S were added at the rate of 3.5 kg and 2.0 kg fresh matter m-2 and their mixtures, +CR+S and +CR+Sw, were incorporated in 3.5 kg of silt loam soil at 60% water-filled pore space (WFPS) and packed in soil microcosms. Nitrous oxide emissions were measured once a day during the 14-day of study period. Daily fluxes of N2O were found to be reduced on +CR+W and +CR+Sw when compared to single-amended +CR treatment. Similarly, N2O fluxes on +CR+Sw (2772 mu g N m-2 h-1) were significantly lower than +CR+S (3606 mu g N m-2 h-1) soon after the amendment but did not vary significantly thereafter. Moreover, the amendment mixture, +CR+S and +Cr+Sw, resulted in lower net N2O emissions by 73.3% and 74.2%, respectively, relative to +CR treatment. While the results clearly suggest that the +CR+S or +CR+Sw reduced N2O emissions, it necessitated further studies, possibly by increasing the frequency of sampling to clarify if washed wheat straw would further mitigate N2O emissions from the vegetable production system.